1. Field of the Invention
The present invention relates, in general, to presses and, specifically, to mechanical presses used in stamping or shearing operations and, more specifically, to control systems for mechanical presses.
2. Description of the Art
Mechanical presses are commonly used to stamp metal parts from flat sheet metal. The press is frequently driven by a large electric motor which turns a large flywheel. This flywheel imparts rotational force to a crank shaft through a clutch which is engaged when operation of the press is desired. The crank shaft drives connecting rods that are connected to a slide section referred to as the upper platen. An upper die that stamps the part being made is attached to the under side of the upper platen and traditionally holds the punches and forms used to form the part being made. A lower die is attached to a generally fixed platform of the press referred to as the lower platen.
In some mechanical presses, the lower platen is not fixed but is made to be movable by means of typically four hydraulic cylinders. These four cylinders perform two general functions. The first function is to act as a dampening system to reduce noise and shock during metal stamping operations. This is done by applying a pressure to the lower platen, through the hydraulic cylinders, that is less than the pressure from the upper platen, thus allowing the motion of the lower platen to slow the progression of the upper platen. This has the overall effect of slowing the breakthrough of the metal and reducing the rate of noise and shock generation. The second function is to provide means for keeping the lower platen parallel to the upper platen during uneven loading of the press platens and frame. In other mechanical presses, the typically four hydraulic cylinders are mounted to the press frame and operate only upon the upper platen, which is fitted with adjustable rods so as to contact the cylinder rods just prior to contact with the material being stamped. Again, the function is to dampen noise and shock generation by slowing the press during metal breakthrough.
As the punch or upper die engages and moves through the metal sheet, forces on the order of several tons are introduced into the dies and the surrounding frame of the press. Such forces progressively increase to a maximum force load at the point of breakthrough of the upper die through the metal sheet. The forces are restrained during the shearing or stamping operation and are stored as distortion or deflection in the dies and in the frame of the press.
These forces are suddenly released when the upper die breaks through the metal sheet resulting in objectionable shock, noise, and vibration. These forces increase correspondingly with the force employed in the stamping or shearing operation. The shock, noise, and vibrations adversely effect the press, surrounding equipment and persons located in the vicinity of the press. Further, these problems occur with each cycle of the press and increase with the force and size of the press.
Because of the noise and shock generated by presses in stamping and shearing operations, presses have been located in an area separated from other manufacturing operations, such as in a separate building or a portion of a large building isolated from other manufacturing operations. This requires shipping, storage, and additional handling of the stamped parts which increases their cost and results in the possibility of damage to the parts.
In order to alleviate or minimize the objectionable characteristics of stamping presses, attempts have been made to decrease the shock, noise, and vibration generated by a press. Such attempts incorporate shock dampening systems into the press which cushion the release of stored forces via a hydraulic; while other systems control the speed of the press during its advance so as to decelerate the press when breakthrough of the work piece occurs. However, such attempts have met with limited success in reducing the shock, noise, and vibration levels generated during a stamping or shearing operation.
Thus, it would be desirable to provide a control apparatus and method for a stamping or shearing press which significantly reduces the shock, noise, and vibration associated with the operation of stamping or shearing presses. It would also be desirable to provide a control apparatus and method for reducing shock, noise, and vibration levels in a stamping press which can be easily adapted to conventional press construction.